RheoMan: a five-year, ERC-funded (Advanced Grant), project to model the rheology of the Earth's mantle

Feb 16, 2015 Leaving Flatland: electron tomography of dislocations Results

Seeing dislocations interacting in 3D: electron tomography elucidates the interaction mechanisms  responsible for strain hardening in olivine single crystals deformed at ca. 0.5 Tm.

See our paper which just appeared in Philosophical Magazine

Seing dislocations in 3D: Electron tomography of dislocations

Small size objects can be reconstructed in 3D using TEM. Tilted series are acquired with high orientation accuracy to ensure constant diffracting conditions. After meticulous alignment to pixel precision, volumes are reconstructed using back projection algorithms.

A more detailed description of electron tomography and electron tomography dedicated for dislocations an be found here


Main results

Contrary to what was thought, a and c dislocations can react.  Figure 1 shows an occurence of a c+a junction. This configuration is rare however. In contrast numerous collinear interactions could be clearly characterized (figure 2). Collinear interaction results from the reaction (leading to annihilation) of two dislocations with opposite Burgers bectors which belong to two different planes. We suggest that the collinear interaction mechanism is a major dislocation interaction mechanism in olivine deformed at temperatures below 1000°C.

 

Figure 1 from Mussi et al. (Philos. Mag., 2015): (a) Micrograph where dislocations [001] are in contrast. (b) Micrograph where dislocations [001] and dislocations [100] are in contrast. (c) The intensity profiles show that the contrast of the yellow dislocation is significantly higher than the two other ones.

 

 

Figure 2 from Mussi et al. (Philos. Mag., 2015): Three orientations corresponding to tilt angles of 46° (a), 22° (b) and -34° (c), with the corresponding stereographic projection on the top right hand corner. The electron transmission reconstructed volume enables us to find the glide planes of the dislocation coloured in green, in red and in blue. They are (1-10), (010) and (140) respectively.

 

Reference: A. Mussi, P. Cordier & S. Demouchy (2015) Characterization of dislocation interactions in olivine using electron tomography Philosophical Magazine 95:335-345. doi: 10.1080/14786435.2014.1000996

 

Note: Flatland: A Romance of Many Dimensions is an 1884 novel by the English writer Edwin A. Abbott. The story describes a two-dimensional world occupied by geometric figures.

Flatland